1. Field of the Invention
This invention relates to a process for producing a compound semiconductor having a desired conduction type region and a semiconductor device obtained by using the same.
2. Related Background Art
In the prior art, for formation of pn junction in compound semiconductors, the liquid phase growth method, the MOCVD method, the MBE method have been practiced. Among them, the liquid phase growth method has been primarily practiced, and therefore description thereof is set forth below by referring to an example.
Liquid phase growth utilizes slow-cooled epitaxial growth, namely difference in the conduction type layers deposited due to difference in temperature.
FIG. 18A shows the carrier concentration distribution near the pn junction of a compound semiconductor formed by the above prior art method. FIG. 18B shows the change in carrier concentration corresponding to the relationship between solution temperature and time. Initially, when the solution temperature is T.sub.1, the region near the substrate is a conductive layer having a high carrier concentration of n-type, and n-type carrier concentration is reduced as the temperature is lowered. And, at the point of the temperature of T.sub.2, the n-p reversal temperature is reached and pn junction is formed. When slow cooling is further continued, p-type layer will grow while becoming higher concentration, until growth is completed at the temperature T.sub.3 by departing the substrate from the solution.
When growth is performed by use of this method, as is apparent from FIG. 18A, the carrier concentration near the pn junction becomes lower, whereby there is the problem that when a device is formed, its response speed becomes delayed.
Also, although it is possible to grow similarly a compound semiconductor crystal by the MOCVD method or the MBE method as previously mentioned, the above methods have not yet been technically established, and cannot be said to be sufficiently reliable.
Further, since the crystal growth by use of the three kinds of methods as mentioned above is epitaxial growth, there is the drawback that an expensive compound semiconductor substrate such as GaAs, etc. must be used as the substrate.
Besides, as to the structures of grown layers, in all of the prior art examples, the pn junction faces will become in parallel to the substrate surface.